The room temperature ethanol gas sensors based on MoS2-CuGaO2 composite prepared by hydrothermal method.

In this paper, MoS2-CuGaO2 composites were successfully synthesized by hydrothermal method. The composites were characterized by X-ray diffraction (XRD), Scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared (FTIR), X-ray photoelectron spectroscopy (XPS), respectively. The specific surface area and pore size distribution were obtained by N2 adsorption-desorption isotherms. The gas sensing property measurements were conducted. The sensitivity of pure CuGaO2 based gas sensor to 100 ppm acetic acid and benzene vapor was 1.4 at 25oC. The sensitivity of MoS2-CuGaO2 composite (M - 5) was 6.0 towards 100 ppm ethanol vapor at 25oC. And the detection limit of MoS2-CuGaO2 (M - 5) based sensor was 0.1 ppm. The results demonstrated that MoS2 had effect on the selectivity and sensitivity of the MoS2-CuGaO2 composites. M - 5 composite is considered to be promising for ethanol sensing application in room temperature.

SnO2QDs sensitized ZnFe2O4spheres with enhanced acetone sensing performance.

Herein, SnO2QDs (<10 nm) with small size instead of conventional nanoparticles was employed to modify ZnFe2O4to synthesize porous and heterogeneous SnO2/ZnFe2O4(ZFSQ) composites for gas sensing. By an immersion process combined with calcination treatment, the resultant porous ZFSQ composites with different contents of SnO2QDs were obtained, and their sensing properties were investigated. Compared with bare ZnFe2O4and SnO2QDs, porous ZFSQ composites based-sensors showed much improved sensor response to acetone. For contrast, the sensor performance of ZFSQ composites was also compared with that of ZnFe2O4sphere modified by SnO2nanoparticles with different size. The porous ZFSQ composite with 5 wt% SnO2QDs (ZFSQ-5) showed a better acetone sensing response than that of other ZFSQ composites, and it exhibited a high response value of 110-100 ppm of acetone and a low detection limit of 0.3 ppm at 240 °C. In addition to the rich heterojunctions and porous structure, the size effect of SnO2QDs was other indispensable reasons for the improved sensor performance. Finally, the ZFSQ-5 composite sensor was attempted to be applied for acetone sensing in exhaled breath, suggesting its great potential in monitoring acetone.

Highly sensitive analysis of trace germanium derived from the efficient electrosynthesis and spectral introduction of GeH4 on foam electrode.

BACKGROUND: The electrochemical hydride generation technology, which uses electrolysis instead of chemical reagents to generate reducing species to achieve gaseous transformation and sample introduction of the tested elements, has received widespread attention in the field of atomic spectroscopy due to its simple, economical, and green characteristics. However, limited by the effective area of the electrode, the introduction efficiency and spectral signal of most elements (e.g., germanium) in practical applications are lower than traditional chemical hydride generation. RESULTS: In this paper, an efficient electrochemical hydride generation (EHG) method based on metal foam electrode for µg L-1 level germanium was constructed. Systematic electrochemical and spectral tests showed that the low charge transfer resistance and the high electrochemical activity of nickel-based foam electrodes jointly promoted the efficient electroreduction of Ge(IV). Besides, the porous network structure of the metal foam material improves the contact probability of reactants while reducing the gas-evolution effect caused by bubble accumulation. Interestingly, adequate reaction sites are crucial for the conversion of germanium, but large foam electrodes are not always compatible with analytical performance. After coupling atomic fluorescence spectroscopy, this new electrolysis method has been proven to be suitable for efficient conversion and quantitative detection of Ge over a wide concentration range (5-150 µg L-1). SIGNIFICANCE: Our proposal to improve the electrosynthesis efficiency of germanane (GeH4) by using metal foam electrode is extremely effective for the detection of trace or ultra-trace germanium. The exploration of electrode material, structure, and especially effective area will also provide ideas for the establishment of highly sensitive analysis methods in the future.

Flexible Synergistic MoS2 Quantum Dots/PEDOT: PSS Film Sensor for Acetaldehyde Sensing at Room Temperature.

Acetaldehyde (CH3CHO) is known as a primary carcinogen, and the development of wearable gas sensors for its detection at room temperature has rarely been rarely reported. Herein, MoS2 quantum dots (MoS2 QDs) have been employed to dope with poly(3,4-ethylenedioxythiophene): polystyrenesulfonate (PEDOT: PSS) via a simple in situ polymerization technique, and the CH3CHO gas-sensing properties of the resultant flexible and transparent film were investigated. MoS2 QDs had been evenly dispersed into the polymer, and it was shown that PEDOT: PSS doped with the 20 wt % MoS2 QDs sensor exhibited the highest response value of 78.8% against 100 ppm CH3CHO and its detection limit reached 1 ppm. Moreover, the sensor response remained stable for more than 3 months. In particular, the different bending angles (from 60 to 240°) had little effect on the sensor response to CH3CHO. The possible reason for the enhanced sensing properties was attributed to the large number of reaction sites on the MoS2 QDs and the direct charge transfer between the MoS2 QDs and PEDOT: PSS. This work suggested a platform to inspire MoS2 QDs-doping PEDOT: PSS materials as wearable gas sensors for highly sensitive chemoresistive sensors to detect CH3CHO at room temperature.

Tough and Antifreezing MXene@Au Hydrogel for Low-Temperature Trimethylamine Gas Sensing.

Trimethylamine (TMA) is one of the important chemical indexes to judge the freshness of marine fish. It is necessary to develop a low temperature TMA sensor to help the monitoring and prediction of the quality of marine fish in cold chain. Herein, a flexible low temperature TMA gas sensor featuring antifreezing and superior mechanical properties was developed based on the Au nanoparticle-modified MXene (MXene@Au) composite. MXene@Au was synthesized and then polymerized with a hydrogel composed of acrylamide (AM), N,N'-methylenebisacrylamide (BIS), sodium carboxymethyl cellulose (CMC), and EG, and the resultant MXene@Au hydrogel was found to exhibit excellent antifreezing performance even at extremely low temperature as well as high tensile strength, ultrastretchability, and toughness, which enabled an efficient gas sensing platform for TMA detection at low temperature. The TMA sensing properties of the flexible MXene@Au DN hydrogel sensor at 25 °C and a low temperature of 0 °C were studied, and a linear relationship between TMA sensitivity and concentration was built. The excellent sensing properties were maintained even under deformation. The application of the MXene@Au DN hydrogel sensor in detection of fish freshness at 0 °C was investigated. The result indicated the potential application of the flexible MXene@Au DN hydrogel gas sensor in dynamic quality monitoring and prediction of marine fish products during its transportation and storage in the cold chain.

Dual-potential electrochemiluminescence of single luminophore for detection of biomarker based on black phosphorus quantum dots as co-reactant.

Simultaneous cathodic and anodic electrochemiluminescence (ECL) emissions of needle-like nanostructures of Ru(bpy)32+ (RuNDs) as the only luminophore are reported based on different co-reactants. Cathodic ECL was attained from RuNDs/K2S2O8 system, while anodic ECL was achieved from RuNDs/black phosphorus quantum dots (BPQDs) system. Ferrocene attached to the hairpin DNA could quench the cathodic and anodic ECL simultaneously. Subsequently, the ECL signals recovered in the presence of tumor marker mucin 1 (MUC1), which made it possible to quantitatively detect MUC1. The variation of ECL signal was related linearly to the concentrations of MUC1 in the range 20 pg mL-1 to 10 ng mL-1, and the detection limits were calculated to 2.5 pg mL-1 (anodic system, 3σ) and 6.2 pg mL-1 (cathodic system, 3σ), respectively. The recoveries were 97.0%, 105%, and 95.2% obtained from three human serum samples, and the relative standard deviation (RSD) is 5.3%. As a proof of concept, this work realized simultaneous ECL emission of  a single luminophore, which initiates a new thought in biomarker ECL detection beyond the traditional ones. Simultaneous cathodic and anodic ECL emissions of RuNDs were reported based on different co-reactants. Ferrocene could quench the ECL emission in the cathode and the anode simultaneously. Thus, an aptasensor was constructed based on the variation of ECL intensity. As a proof of concept, this work realized simultaneous ECL emission of a single luminophore, which initiates a new thought in biomarker ECL detection beyond the traditional ones by avoiding the false positive signals.

First-principles study of pristine and Li-doped borophene as a candidate to detect and scavenge SO2gas.

In this research, the potential application of borophene as gas sensor device is explored. The first-principles theory is employed to investigate the sensing performance of pristine and Li-doped borophene for SO2and five main atmospheric gases (including CH4, CO2, N2, CO and H2). All gases are found to be adsorbed weakly on pristine borophene, which shows weak physical interaction between the pristine borophene and gases. The gas adsorption performance of borophene is improved by the doping of Li atom. The results of adsorption energy suggest that Li-borophene exhibits high selectivity to SO2molecule. Moreover, analyses of the charge transfer, density of states and work function also confirm the introduction of Li adatom on borophene significantly enhances the selectivity and sensitivity to SO2. In addition, desorption time of gas from pristine and Li doped borophene indicates the Li-borophene has good desorption characteristics for SO2molecule at high temperatures. This research would be helpful for understanding the influence of Li doping on borophene and presents the potential application of Li-borophene as a SO2gas sensor or scavenger.

An electrogenerated chemiluminescence aptasensor for lysozyme based on the interaction between Ru(bpy)3 2+ and cucurbit[8]uril.

Strong anodic Ru(bpy)3 2+ electrogenerated chemiluminescence (ECL) was obtained at a cucurbil[8]uril (CB[8]) modified electrode in neutral conditions without the need of an additional coreactant. An ECL aptasensor was fabricated based on the strong ECL emission as well as the host-guest interaction between DNA and CB[8]. Firstly, amino group-terminated complementary DNA (DNA-NH2 ) was firmly immobilized on CB[8]/glass carbon electrode, which could further increase ECL intensity. Then, a ferrocene group-terminated lysozyme aptamer (Fc-DNA) was hybridized with complementary DNA. The inhibiting effect of ferrocene on Ru(bpy)3 2+ ECL resulted in the apparent decrease in ECL signal. When the modified electrode was incubated in lysozyme, specific binding between lysozyme and its aptamer could release the ferrocene group from the electrode surface, and the ECL emission was recovered. As a result, an 'on-off-on' mode ECL aptasensor for lysozyme was fabricated. In the range 0.14-140 pg ml-1 , the increased ECL intensities exhibited excellent linearity with the logarithm of lysozyme concentrations, and the detection limit was calculated as 0.093 pg ml-1 (3σ). The proposed ECL aptasensor exhibited satisfactory analytical performance, revealing the potential application of CB[n]s in an ECL sensing field.

Density functional theory study of Cu-doped BNNT as highly sensitive and selective gas sensor for carbon monoxide.

The adsorption of CO, CO2, CH4, H2, N2 and N2O on armchair (5,5) boron nitride nanotube (BNNT) with and without the doping of transition metals (TM), i.e. Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu or Zn, was investigated using the density functional theory calculation. The results indicate all the considered gases are physically adsorbed by weak interaction on the pure BNNT, revealing that pure BNNT has poor sensing performance for these gases. TM are then doped in the B or N vacancy of BNNT to improve the sensitivity and selectivity. As a result, it was found that the gas adsorption performance of BNNT is obviously enhanced due to the introduction of TM dopant atom. In particularly, according to the results of adsorption energy, Cu doped BNNT (Cu-BNNT) system shows a high selectivity toward CO molecule compared with other metal doped systems. This is further confirmed by the density of state, energy gap and charge transfer analyses. Furthermore, based on the sensor performance analysis, it was found that Cu-BNNT also has favorable desorption characteristics for CO. Therefore, this study concluded that Cu-BNNT can be used as a superior sensor material with high sensitivity, selectivity and favorable recycle time for CO gas.

Electrogenerated chemiluminescence of Ru(bpy)32+ at MoS2 nanosheets modified electrode and its application in the sensitive detection of dopamine.

Electrogenerated chemiluminescence (ECL) of Ru(bpy)32+ was studied at a MoS2 nanosheets modified glassy carbon electrode (MoS2NS/GCE) in neutral condition. Electrochemical results revealed that MoS2 nanosheets could significantly catalyze the electrochemical oxidation of Ru(bpy)32+, as a result, strong anodic ECL was obtained. Several impact factors, such as the modified amount of MoS2 nanosheets suspension, the pH value, and the concentration of Ru(bpy)32+, were investigated to obtain the optimal experimental condition. Dopamine exhibited apparent inhibiting effect on ECL intensity of Ru(bpy)32+-MoS2 nanosheets through energy transfer process, and could be sensitively detected in the range of 1.0 × 10-9 to 1.0 × 10-4 mol L-1. The linear equation between the decrease of ECL intensity and the logthium of dopamine concentration was determined as ΔI = 9965.02 + 1077.03lgC (C in mol L-1), with the detection of 8.5 × 10-10 mol L-1 (3σ). The modified electrode exhibited satisfactory sensitivity, selectivity, and stability, which can be used to detect dopamine in real samples.

Electrochemiluminescence resonance energy transfer between luminol and black phosphorus nanosheets for the detection of trypsin via the "off-on-off" switch mode.

In this work, the electrochemiluminescence (ECL) behavior of a luminol-H2O2 system was studied on a black phosphorus nanosheet (BPN) modified electrode. A quenching effect of BPNs on luminol ECL was achieved based on ECL resonance energy transfer (ECL-RET) with excited state luminol as the energy donor and BPNs as the energy acceptor. Protamine could bind on the surface of BPNs through electrostatic interactions, which can cut off the energy transfer route between luminol and BPNs to restore the ECL signal. The immobilized protamine could be hydrolyzed by trypsin, as a result, the BPN surface was exposed and RET occurred again, resulting in an instant decrease in the ECL intensity. The reduced ECL signals varied linearly with trypsin concentrations, and could be indirectly used in the sensitive detection of trypsin in the range of 100 ng mL-1 to 5 µg mL-1. The detection limit of the biosensor was calculated at levels down to 6.33 × 10-8 g mL-1 (3σ). The proposed ECL sensor was successfully used in the detection of trypsin in serum samples. The results reveal a novel quenching effect of BP nanomaterials on ECL, which will further expand its application in ECL biosensing for proteins.

Electrogenerated chemiluminescence aptasensor for lysozyme based on copolymer nanospheres encapsulated black phosphorus quantum dots.

Black phosphorus quantum dots (BPQDs) can react with Ru(bpy)32+ to generate strong anodic electrogenerated chemiluminescence (ECL). However, the instability and the lack of functional groups on BPQDs limit its further application in the fabrication of ECL biosensor. In the present work, uniform BPQDs-styrene-acrylamide (St-AAm) nanospheres (BSAN) are synthesized by encapsulating BPQDs into St-AAm copolymer nanospheres. Sufficient amount of BPQDs can be embedded into nanospheres, and react with Ru(bpy)32+ to generate strong anodic ECL which is comparable to that of pure BPQDs. Amino group of polymer endows BPQDs the ability to connect with DNA, and can be used to fabricate ECL aptasensor for the sensitive detection of lysozyme. The proposed aptasensor shows high sensitivity, good selectivity and stability for the detection of lysozyme in the range of 0.1-100 pg mL-1 with a detection limit of 0.029 pg mL-1 (3σ). The proposed method reveals the promising ECL sensing application of BP nanomaterials in the detection of various proteins.

Fast response-recovery time toward acetone by a sensor prepared with Pd doped WO3 nanosheets.

Pd-WO3 nanosheets were synthesized through a one-step hydrothermal method using Na2PdCl4 solution as the palladium source and sodium tungstate as the tungsten source, and were used to detect acetone. After being characterized by TEM, XRD, BET and XPS, it was found that Pd doped on the surface of WO3 nanosheets was mainly present as metal palladium, and the specific surface area increased after doping. In addition, the effect of Pd doping on gas sensing properties was studied. When the Pd-doped amount was 2 at%, sensors fabricated with the composites had the best gas sensing performance. Under a 100 ppm acetone atmosphere, the response time was 1 s and the recovery time was 9 s. The detection limit for acetone was 50 ppb at the optimum working temperature of 300 °C, and the selectivity for acetone was excellent under 100 ppm atmosphere (S acetone/S ethanol = 5.06). The excellent gas sensing properties of this material are mainly attributed to the high catalytic activity and the catalytic spill-over effect of the Pd nanoparticles, which provided additional active sites for the sensitive materials.

Enhancement of electrogenerated chemiluminescence of luminol by ascorbic acid at gold nanoparticle/graphene modified glassy carbon electrode.

Gold nanoparticle/graphene (GNP/GR) nanocomposite was one-pot synthesized from water soluble graphene and HAuCl4 by hydrothermal method and characterized by TEM, Raman spectroscopy, XRD, XPS, UV-vis spectroscopy, and electrochemical impedance spectroscopy (EIS). Electrogenerated chemiluminescence (ECL) of luminol was investigated at the GNP/GR modified glassy carbon electrode (GNP/GR/GCE) and the GNP modified glassy carbon electrode (GNP/GCE) in aqueous solution respectively. The results revealed that one strong anodic ECL peak could be observed at ∼0.8 V at two modified electrodes compared with that at the bare electrode. The intensity of the anodic ECL at the GNP/GR/GCE is weaker than that at the GNP/GCE, which should be due to the synergic effect of the enhancing effect of gold nanoparticles and the inhibiting effect of graphene on anodic luminol ECL. One strong cathodic ECL peak located at ∼-0.8 V could be observed at the GNP/GR/GCE but not at the GNP/GCE, which should be result from the adsorbed oxygen at the graphene film. In the presence of ascorbic acid, the anodic ECL at the GNP/GR/GCE was enhanced more than 8-times, which is more apparent than that at the GNP/GCE. Whereas, the cathodic ECL peak was seriously inhibited at the GNP/GR/GCE. The enhanced ECL intensity at the GNP/GR/GCE varied linearly with the logarithm of ascorbic acid concentration in the range of 1.0 × 10(-8) to 1.0 × 10(-6)mol L(-1) with a detection limit of 1.0 × 10(-9) mol L(-1). The possible ECL mechanism was also discussed.

Electrogenerated chemiluminescence of bismuth sulfide nanorods modified electrode in alkaline aqueous solution.

Electrogenerated chemiluminescence (ECL) behavior of a bismuth sulfide nanorods modified glassy carbon electrode (NR-GCE) was investigated in alkaline aqueous solution for the first time. One weak ECL peak of the NR-GCE was observed around -1.70 V when the electrode potential was scanned from 0.0 V to -2.0 V. The intensity of the ECL peak was enhanced greatly in the presence of either H2O2 or persulfate. The dissolved oxygen, the pH and the supporting electrolytes of the working solution could influence ECL emission noticeably. Under the optimal conditions, the ECL signal displayed a good linear relationship with the concentration of hydrogen peroxide in the range of 5.0 × 10(-7) to 1.0 × 10(-4) mol L(-1) with a correlation coefficient of 0.997 and a detection limit of 2.0 × 10(-7) mol L(-1) at the signal-to-noise ratio of 3. A possible ECL mechanism of the NR-GCE was also proposed.

Evaluation of a new electrolytic cold vapor generation system for mercury determination by AFS.

In this study we firstly report a new electrolytic cold vapor generation system for mercury determination on Pt/Ti cathode in the presence of organic acid catholyte. Comparing with the traditional inorganic acid, formic acid increased the signal intensity of Hg vapor from electrolytic generation on Pt cathode and reduced the impact of cathode erosion on the stability of signal intensity. Moreover, formic acid has better interference tolerance. The introduction location for carrier gas is probably the most important factor that influences the signal intensity of Hg from electrolytic vapor generation. The effects of the electrolytic conditions and interference ions on the ECVG have been studied. Under the optimized conditions, the detection limit (3 sigma) of Hg (II) in aqueous solutions is 1.4 ng L(-1); a relative standard deviation of 2.3% for 1 microg L(-1) Hg was obtained. The accuracy of this method was verified by the determination of mercury in the certified reference materials. This system has been applied satisfactorily to the determination of Hg in Traditional Chinese Medicines samples.